This invention relates generally to an active noise control system for attenuating noise emanating from an air induction system of an internal combustion engine.
Internal combustion engines include intake and exhaust valves that rapidly open at specific intervals to introduce a fuel air mixture into a combustion chamber, and to subsequently exhaust waste gases. A major source of noise emanating from an engine is generated from the sudden opening and closing of the intake and exhaust valves during the combustion cycle. The sudden opening and closing of the intake and exhaust valves create acoustic waves due to inertia of the gas streams in the connected passages. A compression zone created near the suddenly closed valve caused by the continued inertia of the incoming stream of the gases propagates an acoustic wave back through the intake manifold passages. This emanates from the air intake inlet as undesirable noise.
Prior art systems for actively controlling the undesirable noise emanating from the air intake include a loudspeaker for generating a sound out of phase with the noise emanating from the air intake system. A microphone disposed near the air inlet detects the noise within the air induction system and a controller generates an input to the loudspeaker to create a sound out of phase with the noise from the engine. The out of phase sound generated by the loudspeaker cancels a substantial amount of audible noise. However, these systems are limited by practical application limitations including speaker size and available power limitations.
Size limitations are most dramatic for active noise control systems used to abate noises at lower frequencies. Typically, the lower frequency noise emanating from the air intake manifold are the most undesirable, while also being the most difficult to abate.
Accordingly, it is desirable to develop an active noise control system able to abate the undesirable lower frequency noises within practical size and power limitations of the loudspeaker.